Extraction of water-soluble organic acids



Dec. 7, 1954 c. s. GODDIN, JR 2,695,494

EXTRACTIQN OF WATER-SOLUBLE ORGANIC ACIDS Filed Dec. 13, 1949 Acids Feed 7 JNVENTOR.

Clifton S.Goddin,Jr.

ATTORNEY miscibility of the solvent in the water layer.

United States Patent r 01th:, assignor to Stmiblind @lulsa; Okla., a "corporation of Application December 13, "seams. 61.260456;

The present invention relates to 'a m'e't hod traction of organic acids from crude mixtureg tiie ie oi .More'part1cularly, 1t pertains to a procedure for prevent mg -the accurr 1ulat1on of objectionable cohcentratio'ns'of coi ittaminants 1n thje'extractionsystemi w e recovery o organic acids from their crude ous mixtures by the useof 'afrela tively'watei inso iii bie solvent-has been ;practiced-for'so'me time; and in batchtype 'OPClfllllOllS or in continuous operations with relattvely pure acid solutions, 'no serious problem 'arises 'in so far as concerns the maintenance of theextraction solv entin astate suiiiciently pureto extract such acids 'efficlently. --I1 1 continuous operations, 'however;-'when ex- .tractmg; acids containing non' aci'dic" impurities; 'such' as for example, alcohols and carbonyl compounds, a prob lem arises due to 'steady'accumulation'of impurities in the solvent with resultant impairment in .eifi'ciency'of the extraction-system: Thus, fdifiicultie's' of this nature have been encountered in 'thefiextraction" of water-soluble ac ds produced as a by-pr'oduct of the"hydrocar'bons'ynthes s process. Thegcrude'prirnary"water fror'n' the 'synthesis react1on constitutes a dilute aqueous'miiiture of acids, alcohols, aldehydes, ketones,"and'esters;' By-a topping operation, thebulk of the nomaeidic chemicals can be removed, and an aqueous acidic bottoms is produced which conta ns smallamount's of ethanohpropanol acetone, and; other impurities. Ethyl'aceta'te has'beeii found to be a suitable solvent for extracting the acids fron lhtllte dtlutesolutions of this type.

1 e carrying out investigations on the co t'nrecovery of such acids using conditions'astaughtb iStl i r s it was observedthat there was a relatively' ra'pid a'cc'umu lat1on of light ltnpurities' in "the solvent "system; Such accumulatlonof impurities, if allowed to continue would not only reduce the extraction efii'ciency of the solvent but also would eventually lead toco'rnplete inoprability of the system. In this connection," one 'ofthe'major impurities accumulating in the system was found to be ethanol. The presence of'ethaiiol'increases the miscibility of ethyl acetateandwater; and, ifbuild-up of ethanol in the solvent is allowed'to" approach to weight per cent, complete miscibility of ethyl acetate and water results, destroymg the extractive action. When ern ploymg ethylacetate. as the solvent, this problem becomes further complicated, owing to partial hydrolysis thereof to ethanol and. acetic acid, thereby tending to increase the Accordingly, it is an object of m invention t I contmuously, by. the use-of a suitable solven i fi t ei soluble carboxyl1c acids from aqfieoiis mixtures thereof containing 1mpur1t1es which boil below or which azeotrope with such solvent, while maintaining the solvent utilized in the extraction step in a state of high purity It IS a further ObJCt of my invention to provide a method for the recovery of water-soluble carboxylic acids from crude aqueous mixtures thereof containing light impurities, by means of a substantially water-insoluble solvent whereby the portion of the solvent solubilized in the ratfinate fraction of the original crude mixture may be readily and continuously separated therefrom in substant ally pure form. It is a still further object to provide a simple, economical method involving the continuous reiitifglOllugftlmgulliltles froin the solvent extraction system s an ta com purified formy pete recovery of the solvent 1n Broadly, my invention comprises sub'ectin a c aqueous mixture of the water-soluble C aIbOX YIiC :i ci d:

"ice

to extraction with a suitable substantially water-insoluble solvent and thereafter recovering the acids from the resulting extract by distilling the latter to obtain one fraction comprising essentially the solvent-employed together with low-boiling contaminants and a second fraction containing thedesired=acidsand high-boiling impurities, which" can thenbe separated from" the acids by further purification steps. The firstfraction, comprising solvent and. low-boiling "impurities, is combined with make-up solvent and recycled to the extraction step. The raftinate layer fromthe original extraction step contains the bulk ot'th e 'low-b'oiling'impurities originally" present in thefc'rudeacid; mixture together with an appreciable quantity of solubilized solvent; This'aqueous raffinate is introduced intoajdistillation column where'the bulk of the water is-rejected t'rom;the system .as bottoms together with any high-boilmg impurities that-might be present. "The overhead traction obtained in this operanon contains-solvent, water, and low boiling impurities. After, permittingithis vtraction tostratify, the upper solvent layer is recycled to the extraction, column and the lower aqueous layer containing the ma or portion of lowboiling impuritiesoriginally present in the crude acid mixture is. withdrawn trom the system and sub ected to an'extractive distillation operation using water as the extractive agent in accordance with Known techniques whereby the solvent is obtained in substantially pure form as. an loverneadstream white a.dilute.aqueous. solution of the low-boilingiimpuritiesis washed down the column andre ec'tedl j 1 .Ylhe process of. myinve'ntionm'ay be usedin conjunction. with/numerous.systems'employed.in the recovery and purification or .carboxylic acids wherein thepresence of substantial concentrations ot'Txlow-boiling .impurities interreres .with the proper. function of the solvent. My invention is. particularly. adapted to. the. recovery of watersoluble acids. produced along .with other. oxygenatedorganic chemical components in the hydrogenation of carbon monoxide in. the presence of a fluidized. alkali-promoted iron. catalyst. under-known. synthesis conditions. In recoveringtthe.water-soluble chemicals found in the aqueous t'raction produced by the reaction of carbon monoxidewwithhydrogen, referred to .above, the entire fraction is-subjected ttoatopping operation in...which the bulk ofthe=non-acid chemicals is taken. overhead andfurther 'processed,...'while the acid. components. of .this fraction, together with a minor portion of the non-acid chemicals, are removed fromthecolumn as. a dilute (about .4 to 6 weight percent acids)v aqueous bottoms... It is bottoms fractions of this general type which are contemplated as feed stocks in carrying out.:the process of. my. invention. -While feed stocks of this type contain numerous impurities, the ones which cause difficulty due to. accumulation in the continuous extraction system are those which boil below the boiling point of the solvent employed, those which-form azeotropes with the. solvent, and those which form with other impurities azeotropes :boiling below the boiling point of such solvent. For convenience, impuritiescorning within .any of the three classifications-noted above are herein referred to as lowboiling contaminants-or-asflow-boiling impurities. The difficulty of purifying the solvent by conventional distillation methods can befurther appreciated by.referenceto the table below, in which theiboiling points of common impuritiles are compared with that of the solvent (ethyl acetate). It will be understood that the impurities are shown merely as typical of those encountered and are to be in no way construed as limiting the scope of my invention.

Component: B. P., C. Acetone-methanol 55.7 Methanol 64.7 Butyraldehyde-ethanol-water 67.2 Ethyl acetate-ethanol-water 70.3 Ethyl acetate-water 70.4 Methyl ethyl ketone-ethanol-water 73.2 Methyl ethyl ketone-water 73.5 Ethyl acetate 77.1

One of the outstanding and surprising features of my invention resides in the discovery that extraction systems of the type here involved can be eflectively maintained in a state of high efficiency merely by" periodically or continuously removing from the system the small amount of water layer obtained by distillation of the aqueous raflinate produced in the extraction step. In normal operation, this water layer amounts to about 1 per cent of the solvent circulation rate. In the conventional solvent acid recovery process, this water layer is recycled within the system and the impurities gradually accumulate in the solvent. it has unexpectedly been found that the objectionable light impurities occur in higher concentration in the water layer and that, by withdrawal of the aforesaid water layer, build-up of light impurities throughout the solvent system can be prevented. It has been found further that by subjecting the water layer to extractive distillation, using water as an extractive agent, the solvent can be easily and continuously separated from the light impurities and returned to the system.

For a better understanding of my invention, reference is made to the accompanying flow diagram, in which a crude aqueous acidic feed is introduced through line 2 to extraction column 4 at an hourly rate of 190 pounds of high-boiling impurities, 138 pounds of low-boiling impuritiles, 5,611 pounds of acids (chiefly acetic, propionic, and butyric acids), and 139,900 pounds of water.

The extraction solvent is introduced near the bottom of column 4 through line 6 at a rate corresponding to a solvent aqueous feed ratio of 1.5. The extract rich in acids is withdrawn through line 8 and introduced into acid stripping column 10. Column 10 is operated at a bottoms temperature of about 131 C. to, insure the substantially complete removal of ethyl acetate from the column as a component of the overhead stream. The resulting bottoms acid fraction, together with high-boiling impurities, is withdrawn through line 12. The overhead stream from column 10, containing chiefly ethyl acetate and water, is withdrawn through line 14 and condenser 16, a portion of the stream being returned to the top of the column as reflux through line 18 and the remainder combined with solvent (ethyl acetate) in line 6 and make-up ethyl acetate from line 24 and recycled to extraction column 4. The aqueous bottoms from .extraction column 4, which contains some ethyl acetate, light impurities, and unextracted acids, is withdrawn through line 26 and introduced into stripping column 28. In the operation of column 28, a bottoms fraction comprising the bulk of the water in the system is withdrawn through line 29 and run to the sewer. An overhead stream, consisting chiefly of ethyl acetate, water, and some light impurities, is withdrawn through line 30 and condenser 32, introduced into separator 34, and allowed to stratify into two layers. The upper solvent layer is withdrawn from separator 34 through line 36 at an hourly rate of 695 pounds of low-boiling impurities, 760 pounds of water, and 12,164 pounds of ethyl acetate, while the lower aqueous layer is withdrawn through line 37 and introduced into extractive distillation column 40 at an hourly rate of 138 pounds of low-boiling impurities, 1,495

lines 6 and 36 and recycled to extraction column 4. The lower aqueous layer in separator 48 is withdrawn through line 52 and returned to column 40 via line 37. The bottoms from column 40 consists chiefly of low-boiling contaminants and water and is withdrawn through line 54 at an hourly rate of 138 pounds of low-boiling contaminants and 7,458 pounds of water.

The description given immediately above is merely illustrative of one embodiment of my invention, and it is to be strictly understood that this invention is not limited thereto. For example, solvents other than ethyl acetate may be employed, such as propyl acetate, isopropyl ether, or any of the other known substantially water-insoluble acid solvents or mixtures thereof boiling sutficiently below acetic acid to permit satisfactory separation of the solvent from the acid by fractional distillation. Other modifications in the process of my invention which would normally occur to those skilled in the art are to be construed as lying within the scope thereof.

I claim:

1. In a continuous process for the recovery of watersoluble, organic, carboxylic acids from a crude aqueous mixture thereof containing low-boiling, water-soluble, non-acid, oxygenated, organic compounds as contaminants, the steps which comprise subjecting said crude mixture to extraction with a substantially water-insoluble solvent for said acids and boiling substantially below the boiling point of any of such acids, distilling the resulting aqueous raflinate from the aforesaid extraction step; collecting an overhead fraction comprising solvent, water and low-boiling contaminants soluble in said solvent and a bottoms fraction consisting essentially of water, allowing said overhead to stratify into an upper solvent layer containing a minor amount of said low-boiling impurities with respect to the solvent present in said upper layer and a lower aqueous layer containing said low-boiling impurities, returning said upper solvent layer to the abovementioned extraction step, and withdrawing said lower aqueous layer from the extraction system.

2. The process of claim 1 in which ethyl acetate is em ployed as the solvent.

3. The process of claim 1 wherein the aqueous mixture of crude acids treated is produced by the hydrogenation of carbon monoxide in the presence of a fluidized alkaline-promoted iron catalyst under known synthesis conditions.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,211,087 Weirnann Aug. 13, 1940 2,419,039 Scarth Apr. 15, 1947 2,430,086 Staff Nov. 4, 1947 2,505,752 Burton May 2, 1950 2,526,508 Scheeline et a1 Oct. 17, 1950 2,563,739 Palm et al Aug. 7, 1951 2,568,717 Burton et al Sept. 25, 1951 2,571,151 McGrath et al Oct. 16, 1951 

1. IN A CONTINUOUS PROCESS FOR THE RECOVERY OF WATERSOLUBLE, ORGANIC, CARBOXYLIC ACIDS FROM A CRUDE AQUEOUS MIXTURE THEREOF CONTAINING LOW-BOILING, WATER-SOLUBLE, NON-ACID, OXYGENATED, ORGANIC COMPOUNDS AS CONTAMINNANTS, THE STEPS WHICH COMPRISES SUBJECTING SAID CRUDE MIXTURE TO EXTRACTION WITH A SUBSTANTIALLY WATER-INSOLUBLE SOLVENT FOR SAID ACIDS AND BOILING SUBSTANTILLY BELOW THE BOILING POINT OF ANY OF SUCH ACIDS, DISTILLING THE RESULTING AQUEOUS RAFFINATE FROM THE AFORESAID EXTRACTION STEP; COLLECTING AN OVERHEAD FRACTION COMPRISING SOLVENT, WATER AND LOW-BOILING CONTAMINANTS SOLUBLE IN SAID SOLVENT AND A BOTTOM FRACTION CONSISTING ESSENTIALLY OF WATER, ALLOWING SAID OVERHEAD TO STRATIFY INTO AN UPPER SOLVENT LAYER CONTAINING A MINOR AMOUNT OF SAID LOW-BOILING IMPURITIES WITH RESPECT TO THE SOLVENT PRESENT IN SAID UPPER LAYER AND A LOW AQUEOUS LAYER CONTAINING SAID LOW-BOILING IMPURITIES, RETURNING SAID UPPER SOLVENT LAYER TO THE ABOVEMENTIONED EXTRACTION STEP, AND WITHDRAWING SAID LOWER AQUEOUS LAYER FROM THE EXTRACTION SYSTEM. 